1. Technical Field
The present invention relates to water-proof and dust-proof membranes, and more particularly to a water-proof and dust-proof membrane assembly that has a supporting member.
2. Description of Related Art
Technical developments improve the quality of human life and make the electronic products essentials to human life. Consumer electronic products, such as cell phones, digital cameras, laptop computers, MP3s, MP4s, and PDAs, or general outdoor electric appliances, such as security monitoring systems, outdoor lamps, traffic lights, underwater electric appliances, marine electric appliances, telecommunication devices and medical electronic devices.
Housings of diverse outdoor electronic products are always subjected to temperature variation, weather corrosion and solar radiation. Also, sudden drop of the ambient temperature would cause unbalanced air pressure in the housing, hence making the air or the moisture enter the housing, and therefore making the electronic circuits, which are sensitive to the air and the moisture, in the housing breakdown due to the corrosion. In addition, those existing consumer electronic products which lack the water-proof and dust-proof capabilities, when splashed by drinks or other liquids accidentally or when frequently used, are likely to get damaged because of the liquids or dust entering into the electronic circuit thereof. Hence, the related manufacturers have paid much attention to continuously improve the existing electronic products in practicability and duration.
For prolonging the service life of electronic products, one major factor is to maintain the internal electronic circuits working normally. To ensure the sensitivity of electronic products, and to secure normal operation of their internal electronic circuit, so as to endow the electronic products with prolonged service life, factors including water-proof capability, dust-proof capability, corrosion resistance and air-permeability have to be thoroughly considered so as to enable the electronic products to remain good operation even in adverse circumstances.
Currently, it is common to use a porous film as a protective membrane. Specifically, most porous films are typically made of fluorinated polymeric material, e.g. fluoropolymers, fluorinated ethylene-propylene (FEP), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), etc.
The PTFE porous film has excellent water repellency at its surface and possess a water contact angle of 118°, being the largest among the above-mentioned materials, so it is unlikely to be wetted by general liquids and unlikely to adhere to other materials. Through disclosed process (for example see U.S. Pat. Nos. 3,953,566, 3,962,153, and 4,902,423) for preparing a PTFE porous film, the PTFE porous film can be made into a porous film with 1 billion to 15 billion micro-pores per square inch, having excellent air-permeability. Furthermore, the micro-pores of the above-mentioned PTFE porous film have an average pore diameter of 0.25 to 0.55 μm, which is only one ten-thousandth as large as a rain drop, yet is 700 times larger than a sweat drop or a vapor particle, so the PTFE porous film is advantageous as being an air permeable and water-proof film.
The internal network structure formed with the microfibers of the PTFE porous film is in nature heat resistant and surface lubricative, and accordingly allows the dust absorbed at its surface to be easily removed. The above-mentioned PTFE porous film can be made with different pore sizes and laminated with various fabrics for applications of materials where dust-proof capability is required. Thus, the PTFE porous film is useful for dust-proof and filtering purposes.
Such a protective membrane made of a PTFE porous film that is water-proof, sound-transmitting, dust-proof and air permeable, when being applied to different products, may have to provide different levels of water-proofness, sound transmittance as well as air-permeability. It is known that the water-proofness of the PTFE porous membrane is enhanced by reducing an average pore size. However, the water-proofness and the air-permeability usually compromise each other's performance, in short, the air-permeability and the water-proofness are in a trade-off relationship. In addition, the sound transmittance and the water-proofness are also in a trade-off relationship. To be brief, a reduced average pore size lowers the air-permeability as well as the sound transmittance. Accordingly, it is not easy to enhance the water-proofness without lowering the air-permeability and the sound transmittance. While there are many commercially available protective membrane products made of a PTFE porous film, one with high air-permeability and high sound transmittance must have a relatively large pore diameter, which suggest weakened water-proofness. On the other hand, one having relatively small pore diameter to present good water-proofness can often suffer from poor air-permeability and poor sound transmittance.
While the aforementioned common electronic products and water-proof electronic products that need a competent protective membrane made of a PTFE porous film for protecting the internal electronic circuits, many non-electronic products with special requirements related to water-proof capability and air-permeability are also in need of such protective membrane. Thus, how to make a protective membrane having satisfactory water-proofness, dust-proof capability, and air-permeability, and being widely adaptive to various products to provide protection and prolong the service life of the products is an issue to be addressed.